KANDAHAR, Afghanistan (Reuters) -- Taliban insurgents killed 25 Afghan civilians, including a child, after firing on one bus and seizing control of another in the southern province of Kandahar, a local police chief said.

Violence in the war-torn country has surged this year with attacks at their highest level in six years, the United Nations' top envoy in Afghanistan said this month. Some 4,000 people have died so far this year, a third of them civilians.

The latest attack, on October 16, happened while two buses carrying passengers, including women and children, drove through Maywand district in Kandahar, the spiritual home of the Taliban and where the hard-line Islamists still draw a lot of support.

The Taliban fighters tried to stop one of the buses but it carried on driving, Kandahar police chief Matiullah Qateh said. The insurgents then fired on the bus, killing a child.

The militants managed to stop the second bus, carrying about 50 passengers, Qateh said. They killed 24 of the travelers and freed the rest, he said.

Although an investigation was launched on October 16, the bodies were only found later some distance from the road, Qateh said.

A spokesman for the Taliban, Qari Yosuf Ahmadi, told Reuters they had killed 27 people he said were Afghan soldiers.

It was not possible to independently verify any of the casualty figures due to poor security and lack of access to the area where the attack took place.

Taliban militants often launch attacks against Afghan and foreign soldiers but the vast majority of those killed, some 80 percent, are Afghan civilians, security experts say.